Volunteers Joan and John Hobbs, and their adult daughters Melissa and Naomi Hobbs have taken part in the bat count for about a decade. Once a month, rain or shine, they have enjoyed standing in the bush and watching the bats fly over.

“We’re retirees – we do it as a community service,” says Joan. “We like being out in nature, and we’ve met many interesting people.”

There are four species of flying fox in Australia. The grey-headed and spectacled flying foxes are listed as vulnerable to extinction under national environment law, while the black and little red flying foxes are not threatened.

Grey-headed flying foxes arrived in Victoria and set up a camp in Melbourne in the 1980s. They were initially viewed with concern, with residents worried about noise, smell and the risk of bats carrying disease (the likelihood of this is extremely low).

By 1986, a large colony had settled in the Royal Botanic Gardens and in 2003 they had to be relocated because they were damaging historically significant trees.

Van der Ree was one of the botanic gardens staff who rose at 4am daily for six months to bang cooking pots and play discordant music in the hope the bats would leave. They eventually moved to Yarra Bend.

Attitudes to the bats have since changed considerably, says van der Ree, and many people love seeing them fly over their homes.

About five years ago, researchers from the Hawkesbury Institute for the Environment at the Western Sydney University noticed flying fox colonies were visible emerging from cloud cover on the Bureau of Meteorology weather radar.

Using archival weather data, they were able to compare manual bat counts with those captured by the radar and found they were similar. The team has also used thermal drones to ascertain numbers.

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“You fly a drone over a colony early in the morning just after the bats have returned, and their bodies are warm,” says ecologist Dr Jessica Meade. “They stand out as little hot white dots against the cooler background of the trees. Then you can count them.”

A new custom-built sprinkler system has been installed by Parks Victoria at Yarra Bend Park for hot days, particularly when temperatures rise above 38 degrees. Fruit bat colonies can be susceptible to mass deaths on days of extreme heat, which are occurring more frequently due to climate change.

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